Capacitors are commonly-used electrical components of semiconductor circuitry. A typical capacitor construction comprises a first conductive plate and a second conductive plate, with a dielectric material between and separating the conductive plates. A typical dielectric material used in capacitor constructions comprises three layers, with a first layer being a silicon dioxide layer, a second layer being a silicon nitride layer, and a third layer being another silicon dioxide layer, with the silicon nitride layer being between the silicon dioxide layers. As silicon nitride has a higher dielectric constant than silicon dioxide, it would be desirable to eliminate one or both of the silicon dioxide layers from capacitor dielectric material.
A prior art method of forming a capacitor is described with reference to FIGS. 1 and 2. Referring first to FIG. 1, a semiconductive wafer fragment 10 is shown at a preliminary step of a prior art processing sequence. Wafer fragment 10 comprises a semiconductive substrate 12 and a first capacitor plate layer 14 overlying substrate 12. Substrate 12 comprises a lightly doped monocrystalline silicon material. First capacitor plate layer 14 typically comprises conductively doped polysilicon. As will be recognized by persons of ordinary skill in the art, first capacitor plate layer 14 need not be formed in direct physical contact with a semiconductive substrate 12.
To aid in interpretation of the claims that follow, the term "semiconductive substrate" is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term "substrate" refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
An oxide layer 16 is formed over first capacitor plate layer 14. Oxide layer 16 is typically native oxide which naturally forms over a polysilicon layer 14 upon exposure to an oxygen-comprising atmosphere.
A silicon nitride layer 18 is formed over silicon oxide layer 16. Silicon nitride layer 18 is commonly formed by chemical vapor deposition and may be formed, for example, utilizing dichlorosilane and ammonia at a pressure of 500 milliTorr and a temperature of 680.degree. C. Silicon nitride layer 18 commonly has a number of pinholes, or pits, 20 extending partially into or through silicon nitride layer 18. Such pits are undesirable as they, if left unfilled, would permit shorting between an outer conductive plate 24 (shown in FIG. 2 and discussed below) and inner conductive plate 14. Accordingly, pits 20 are typically filled.
Referring to FIG. 2, a layer of silicon dioxide 22 is formed over silicon nitride layer 18 and within pits 20 to fill pits 20. Silicon oxide layer 22 is commonly formed by exposing wafer fragment 10 to a wet oxidizing atmosphere at about 850.degree. C.
After formation of silicon oxide layer 22, a second, or outer, conductive plate layer 24 is formed over oxide layer 22 to complete formation of a capacitor structure 30. At least one of capacitor plate layers 14 or 24 is electrically connected to a circuit external of capacitor 30 for charging and discharging capacitor 30.
Another aspect of the prior art pertains to nitridation of silicon surfaces. Such nitridation is commonly utilized to form an insulative layer over silicon services for electrically isolating components of a semiconductor circuit from one another. A prior art nitridation method is described with reference to a wafer fragment 40 in FIG. 3. Wafer fragment 40 comprises a substrate 42, a silicon-comprising conductive layer 44 overlying substrate 42, and a silicon nitride layer 48 overlying conductive layer 44. Substrate 42 may comprise, for example, a lightly doped monocrystalline silicon wafer. Conductive layer 44 may comprise, for example, conductively doped polysilicon. Also, although not shown, an oxide layer may be formed between conductive layer 44 and nitride layer 48 if, for example, conductive layer 44 comprises polysilicon and is exposed to oxygen prior to formation of silicon nitride layer 48.
Silicon nitride layer 48 is formed by exposing a surface of silicon-comprising layer 44 to ammonia at a pressure of less than or equal to one atmosphere and at a temperature of about 1000.degree. C. Such process is self-limiting due to poor diffusion of the nitrogen species through the initially formed layer of silicon nitride (Si.sub.3 N.sub.4). The maximum silicon nitride layer thickness that can be achieved with such process is 35 Angstroms.